Method for retrieving a severed pipe string from a well

ABSTRACT

Method and apparatus for retrieving a severed pipe string remaining in a well including milling apparatus for milling the upper, flattened end of the remaining pipe string in order to prepare the end for grappling by a grappling device and thereafter retrieving the pipe string with the grappling device.

ilnrte tates Patent 1191 [111 3,872,926

Van Gils 5] Mar. 25, 1975 [54] METHOD FOR RETRIEVING A SEVERE!) 3,587,748 6/1971 Kerr 166/301 PIPE STRING FROM A WELL 3,785,690 l/1974 Hutchinson 166/99 X [76] Inventor: Adrianus W. Van Gils, 24

Woodstock Rd, Aberdeen, Scotland '22 Filed: June 13, 1974 [21] Appl. No; 479,118

[52] US. Cl 166/301, 166/98, 29/103, 294/8631 [51] Int. Cl E21b 31/02, E21b 29/00 [58] Field of Search 166/301, 99, 98, 55, 55.1, 166/556, 178, 297, 315

[5 6] References Cited UNITED STATES PATENTS 2,149,417 3/1939 Brown 166/301 Primary Examiner-Stephen J. Novosad [57] ABSTRACT Method and apparatus for retrieving a severed pipe string remaining in a well including milling apparatus for milling the upper, flattened end of the remaining pipe string in order to prepare the end for grappling by a grappling device and thereafter retrieving the pipe string with the grappling device.

5 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION This invention relates to the retrieval of a pipe string from an oil well or the like.

There are occasions in oil well drilling when it is necessary to temporarily sever the drill string and leave the remaining string in the hole for some period and thereafter retrieve it. For example, in offshore drilling operations from a drill rig, there may be several hundred feet of drill string extending from the floating platform to the sea floor, and thousands of feet of drill string extending through the well head blowout preventer stack and down into the well. If an emergency rises such as a blowout, a loss of anchor or the approaching ofa dangerous storm it may be necessary for the rig to move from the well site. This is accomplished by temporarily severing the drill string inside the blowout preventer stack and removing the upper end.

A shear ram type blowout preventer is used to sever the drill string in the blowout preventer stack. Shear ram blowout preventers are very well known and comprise two opposing shear rams mounted in opposing sides of the drill string. When these shear rams are forced together, the drill string is actually sheared. The shearing action of the blowout preventer rams also flattens out the drill string at the point at which the string is severed. This leaves the remaining upper end of the drill string flattened and flared outwardly such that it is difficult for any known type of grappling tool to fish the remaining drill string out of the hole.

SUMMARY OF THE INVENTION It is the object of this invention to provide a new and improved method for retrieving a pipe string remaining in a well as a result of a severing and removal of the upper portion of the string. Such method includes the steps of firstly supporting the pipe string in the blowout preventer stack and secondly, shearing the pipe string and removing the upper portion. A milling device is then run downwardly into the hole and the flattened end of the remaining pipe string is milled until the diameter thereof is equal to or less than the diameter of a joint in the pipe string. The milling device is then removed and a grappling device is lowered about a joint in the remaining pipe string for lifting upwardly and retrieving the pipe string.

It is further an object to provide new and improved apparatus for first milling the flattened, flared upper end of a pipe string remaining in an oil well as the result of some type of severing operation and further to provide apparatus for grappling and retrieving the pipe string after the upper end thereof has been properly prepared. Such milling apparatus includes a milling means for mounting with a top sub assembly which is mounted with a running string or other means for running the milling means into the oil well. The milling apparatus includes means for positioning or guiding the apparatus about the flattened, upper end of the pipe string and further means for milling the flattened, flared upper pipe string end to reduce the diameter thereof to a diameter substantially equal to or less than the diameter of a joint in the remaining pipe string.

A grappling device for raising or retrieving from the well the remaining, severed pipe string is operated in cooperation with the annular blowout preventer rams which support the pipe string at a joint thereof. The grappling device includes a top sub assembly adapted for running into the well by any suitable means and a cylindrical grappling assembly mounted with the top sub, the grappling assembly including a cylindrical grapple member for positioning about and grappling the pipe string at ajoint at which the pipe string is supported. Further, an annular guide member is mounted with the grapple assembly for landing on the annular blowout preventer rams for positioning and aligning the grapple member about the pipe string joint.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view taken through a blowout preventer stack and exposing the upper end of a pipe string which is supported on an annular blowout preventer rams, and further disclosing the milling device of the preferred embodiment of this invention in position for reducing the diameter of the flared, flattened upper end of the pipe string; and

FIG. 2 is a sectional view through the blowout pre' venter stack similar to FIG. 1 with the grappling device of the preferred embodiment of this invention illustrated centered about a joint of the pipe string in position for grappling and retrieving the pipe string.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing,.FIG. 1 illustrates the milling deviceM of the preferred embodiment of this invention in position in blowout preventer stack B to mill the upper flattened, flared end E of a pipe or drill string S remaining in an oil well after severance and removal of the upper portion of the pipe or drill string (not shown). FIG. 2 illustrates the grappling device G of the preferred embodiment of this invention in position to remove the remaining pipe string 5 after the upper end E has been prepared by the milling device M. The Y blowout preventer stack B is well known and includes within the stack casing 10 a shear ram type blowout preventer 11 and an annular blowout preventer 12. The

shear ram blowout preventer 11 is also of standard construction and includes opposing shear rams 11a and 11b which, when actuated by suitable means such as hydraulic power, are driven together to crush and sever the pipe string S in order to prevent the passage of fluid through the chamber 10a of the blowout preventer stack B. The annular blowout preventer 12 is mounted in a well known manner below the shear ram blowout preventer II for providing a sealing off of the annular space between the pipe string S and the inside wall 10b of the blowout preventer stack casing '10.

The annular blowout preventer rams 12a and 12b are well known and include semi-circular grooves (not shown) for forming an opening (not shown) to receive the pipe string S. The diameter of this opening formed by the closed rams 12a and 12b is such that the rams will support the pipe string S at a joint 14. Prior to the closing of the shear rams lla and 11b, the pipe string S is lowered until one of the joints 14 is supported by the rams 12a and 12b ofannular blowout preventer 12. The rams 11a and 11b are then closed to sever the pipe string S and the top severed portion of the pipe string S is removed so that the platform rig can be moved. The remaining pipe string S, is left with the flattened. flared upper end E.

The milling device M of FIG. 1 includes a top sub 15 which may be a separate sub assembly or the pin end of a joint of pipe. In either event, the top sub assembly 15 is lowered or run into the blowout preventer stack casing by any suitable means operated from the surface.

The milling device M further includes a bowl 16 which is generally cylindrical in cross-sectional configuration and is threadedly attached to the top sub assembly at 15a. The bowl 16 includes a cylindrical outer wall 16a and an inner wall 16b which is formed of a continuous tapered, helical groove 16c. Such a bowl 16 is commonly known and used in grapple tools in the oil well industry. It should be understood that other suitable cylindrically shaped structures can be utilized instead of the bowl 16. For example, the bowl 16 can be replaced with a hollow, cylindrical member having both inside and outside walls which are smooth and not grooved. v

A milling section 17 is threadedly mounted at 16d onto the bottom of the bowl 16. The milling section or member 17 has a cylindrical, outer surface 170 of substantially the same diameter as the bowl wall 16a and bottom portion 15b of the top sub assembly 15. However, the milling device 17 includes an internal, tapered, milling surface 19 which is rotated to mill flared ears 18a and 18b off the upper pipe string end E. The internal surface 19 includes a tapered frustro-conical portion 19:: and a substantially straight cylindrical portion (as compared with the longitudinal axis 20 of both the blowout preventer stack B and the milling device M). The internal, tapered conical surface 19a is tapered from a minimum diameter adjacent the straight surface portion 19b to a maximum diameter near the bottom of the milling section 17. The internal surfaces 19a and 1911 are formed of a series of circumferentially spaced milling strips or ribs 19c of a hard, abrasive metal such as a sintered tungsten carbide sold under the trademark Itcoly by Bowen Tools, Inc. Each of the abrasive strips 190 is mounted onto both the straight cylindrical surface portion 19b and the tapered, conical internal surface portion 190. The circumferential spacing of these strips 190 provides a series of circumferentially spaced, longitudinally extending grooves or water courses 19d These water courses 1911' provide for the passage of water downwardly through top sub assembly bore 15c, through the chamber formed by inside bowl housing wall 161), and through the bore formed by the internal, abrasive surface 19 of the milling device 17 and outwardly of the milling section 17 between the upper pipe string end E and the internal tapered surface 19a. In this manner, water or other fluid can be utilized to flush the bits of metal which are milled off the upper end E in order to keep the internal, abrasive surface 19 substantially clean during milling operatrons.

A cylindrical guide member 21 is threadedly mounted at 21a onto the bottom of the milling section 17. The cylindrical guide 21 has an outside surface 21a of a diameter substantially equal to the diameter of the outside mill sections surface 171:. Inside wall or surface 211) ofthe guide member 21 is cylindrical in configuration and has a diameter slightly greater than the outside diameter of the pipe string joint 14 such that the guide member may be lowered over the pipe string joint 14 easily. An annular, brass pad 22 is mounted onto the bottom end 210 of the cylindrical guide member 21.

The annular pad 22 is made of brass or other suitably soft metal or other material, as compared with the hardness of the guide member 21, for preventing damage to the annular blowout preventer rams 12a and 12b upon landing thereon. The effective length of the guide member 21 determined the ultimate, milled diameter of the upper pipe string end E in that further downward movement and further milling by the milling section 17 is prevented by the landing of the guide member 21 with pad 22, onto the tops of the annular blowout preventer rams 12a and 12b. Thus the length 1 may be varied as desired to vary the ultimate and final diameter of the upper pipe string end E, which is illustrated in its final milled form in FIG. 2. In the preferred embodiment of this invention, the final diameter of the milled upper pipe string end E is slightly less than the outer di ameter of the pipe string joint 14.

After the milling operation is completed and the outside diameter of the upper pipe end E has been milled down to a diameter slightly less than the string joint diameter 14, the milling device M is removed from the blowout preventer stack B.

The grappling device G of FIG. 2 is then utilized to retrieve the pipe string S. The grappling device G also includes atop sub assembly 30, which is basically identical to the top sub assembly 15 of the milling device M. Thus the top sub assembly 30 can be the pin end of a drill pipe joint. An extension sub 31, which is a hollow, cylindrical connecting member, is threadedly attached at 31a to the top sub assembly 30. Outside wall 31b of the extension sub has the same diameter as base 300 of the top sub assembly 30. The diameter of the inner extension sub wall 31c is greater than the diameter of the milled pipe end E illustrated in FIG. 2 and is thus adapted to receive the mill pipe end E as described hereinafter.

A cylindrical member or bowl 33 similar to the bowl 16 is threadedly mounted at 33a onto the extension sub 31. The bowl 33 has an outer diameter formed by outside wall 33b equal to the diameter of the outer extension sub wall 31b. The bowl 33 is a well known type of grapple bowl and has an inside surface or wall 33c formed with a continuous, spiraled, helical groove 33d therein with tapered wall portions. The bowl 33 is utilized to mount a typical basket grapple member 34 therein for gripping the pipe string joint 14. The basket grapple member 34 is also well known in the industry and is basically of one-piece construction includes a series of upwardly extending fingers such as 34a which cooperate to form a spiral groove on the outer wall 34b thereof for mounting the basket grapple member 34 in the corresponding spiral groove 33d in the inside spiralgrooved wall 33c of the bowl 33. The upwardly extending grapple fingers 34a have a series of gripping ridges 34c machined therein in order to grip the drill string joint 14.

A landing guide member 35 is threadedly attached at 35a to the bottom of the bowl 33. The landing guide member 35 is substantially cylindrical and has an inner diameter larger than the diameter of the pipe string joint 14. A landing pad 35b ofa soft metal such as brass is mounted onto bottom annular face 35c of the landing guide member 35 for preventing damage to the annular blowout preventer rams 12a and 12b. A mill control packer 36 mounted onto the top annular face 35e of the landing guide member 35 and includes an inner seal ring 37 having a diameter sufficient to resiliently and sealably engage the pipe string joint 14. The mill control packer 36 is utilized to prevent the passage of fluid between the bowl 33 and the pipe string joint 14 such that any fluid circulating through top sub assembly central bore or passageway 30b is forced into the severed drill string S during the removal of the drill string S by the grappling device G. The effective length 1 of the landing guide member 35, including the landing pad 35b, is sufficient to center and position the grapple member 34 about the pipe string joint 14 upon engagement of the landing pad 35b onto the top of the annular blowout preventer ram 12a and 12b. in this manner, the grapple member 34 is properly centered to grip the pipe string joint 14 such that the annular blowout preventer rams 12a and 12b can be released and withdrawn thereby freeing the grappling device G to re trieve the severed and remaining pipe string S from the well.

OPERATION AND USE As previously mentioned, the apparatus and method of this invention can be utilized to retrieve the remaining pipe string S whenever it is necessary to leave the pipe string S in the well for some period of time such as under emergency conditions. Whenever it is necessary to sever the pipe string S, the pipe string joint 14 is positioned to seat onto the closed annular blowout preventer rams 12a and 12b. Then the shear ram type blowout preventer 11 is actuated to drive the shear rams llu and 11b together to sever the pipe string positioned therebetween. The rams also crush and flatten the pipe leaving the upper severed end E having a flared appearance with ears 18a and 18b flared outwardly to a diameter probably greater than the diame ter ofthe pipe string tool joint 14. It has been found in the past very difficult to grasp such a flattened upper pipe end E for retrieval of the severed and remaining drill string S.

The milling device M of the preferred embodiment of this invention is lowered downwardly over the upper pipe string end E to about the position illustrated in FIG. 1. The entire milling device M is then rotated from the surface through the top sub assembly such that the inside milling surface 19 mills and reduces the enlarged diameter of the pipe end E as illustrated in FIG. 1. As the milling operation continues, the milling device M is lowered downwardly until the cylindrical guide member 21 with landing pad 22 actually lands on the annular blowout preventer rams 12a and 12b. At this point, the length 1 of the guide member 21 is such that the internal milling surface 19 of the milling section 17 will have milled the upper pipe end E to a diameter slightly less than the diameter of the pipe string joint 14. In other words, whenever the landing guide member 21 with the pad 22 land onto the annular blowout preventer rams 12a and 1212, the upper pipe end E is positioned at a point on the internal, abrasive surface 19 of the milling section 17 which has a diameter slightly less than the diameter of the pipe string joint 15. Thus by varying the length 1 of the guide member 21 with the landing pad 22, the ultimate and final milled diameter of the pipe end E as illustrated in FIG. 2 may be varied as desired. In the preferred embodiment of this invention, it is desirable to mill down the largest diameter, flared portion of the upper pipe end E until the ears 18a and 18b have been substantially removed leaving the pipe end E with a maximum diameter less than the diameter of the pipe string joint 14.

The milling device M is then removed from the blowout preventer stack B and the grappling device G is lowered down into the blowout preventer stack. Since the top sub assembly 15 and 30 are substantially identical, it is possible for; the user to remove the bowl 16 and parts attached therewith from the top sub assembly 15 and to mount thereon the extension sub 31 of the grappling device G with its attached parts thus using the same top sub assembly for both tools. In either event, the grappling device G is lowered down into the blowout preventer stack B in order to grip and remove the pipe string S.

As the grappling device G is lowered downwardly over the prepared upper pipe end E, the pipe end E passed through the mill control packer 36, through the grapple member 34 and into the recess formed by the inside wall 31c of the extension sub 31. The grappling device G is lowered until the landing guide member 35 with pad 35b lands onto the annular blowout preventer rams 12a and 12b. The length 1' of the landing guide member 35 including the landing pad, 35b is designed to position the grapple member 34 about the pipe joint 14 when the guide member 35 and landing pad 35b is landed onto rams 12a and 12b. The entire grappling device G is then pulled upwardly causing the grapple member 34 to grip the pipe string joint 14 in a well known menner and the entire pipe string S is lifted up wardly and removed from the oil well. Although the actual functioning of the grapple member 34 within the bowl 33 is well known, it may be mentioned that the corresponding, spiralled outside wall 34b is cammed against the tapered inside wall portion 33d of the bowl 33 to cause the grapple member 34 to grip the pipe string joint 14. Further lifting of the grappling device G causes even tighter gripping engagement by the grappling member 34 (and fingers 34a thereof) and, when the blowout preventer rams 12a and 12b are with drawn, the pipe string S is free to move upwardly and outwardly of the well.

It should be understood that the actual length 1 ofthe guide member 21 for the milling device M will depend upon the distance between the shear ram type blowout preventer 11 and the annular blowout preventer 12. The larger'the distance between the shear ram type blowout preventer 11 and the annular blowout preventer 1,2, the greater the length 1 of the guide member 21, includes the landing pad 22 necessary to position the desired portion milling surface 19 of milling section 17 over the end E. Further, the degree of incline or taper of the frustro-conically shaped internal abrasive wall portion 19a of the milling device 17 can be varied to further vary the ultimate diameter of the upper pipe end E. Similarily, the length 1' of the guide member 35 of the grappling device G will depend upon the distance between the blowout preventer 11 and 12, the effective length 1 ofthe guide member 35 being such to position the grapple member 34 about this drill string joint 14.

The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the size, shape, and materials as well as in the details of the illustrated construction may be made without departing from the spirit of the invention.

I claim:

1. A method of retrieving a severed pipe string or the like remaining in a well, comprising the steps of:

supporting said pipe string in the blowout preventer stack in the rams of an annular blowout preventer; severing said pipe string above said annular blowout preventer thus forming a flattened upper end on the pipe string remaining in the well in order to remove the top portion ofthe pipe string temporarily; running a milling device down to the flattened pipe string end and milling said end to reduce the diameter thereof; and removing the milling device and lowering a grappling device, over said milled pipe string end and lifting said pipe string from said supported position. 2. The method set forth in claim 1, wherein said remaining drill string is removed by the steps of:

lowering a spiral grapple downwardly over said milled end of said pipe string; positioning said spiral grapple about a pipe joint; and

grappling said remaining pipe string at said pipe joint and raising same.

3. The method set forth in claim 2, including the steps of:

supporting said pipe string at a joint thereof; and

positioning said grapple about said joint by landing the grapple on the rams of said annular blowout preventer.

4. The method set forth in claim 1, including:

milling the flared ears of said flattened drill string end to reduce the diameter of said flattened upper end to less than the diameter of a pipe string joint.

5. The method set forth in claim 1, including:

supporting said pipe string at by joint thereof; and

limiting the final, milled diameter to the flattened pipe string end by landing the milling device on said blowout preventer rams.

I =l l 

1. A method of retrieving a severed pipe string or the like remaining in a well, comprising the steps of: supporting said pipe string in the blowout preventer stack in the rams of an annular blowout preventer; severing said pipe string above said annular blowout preventer thus forming a flattened upper end on the pipe string remaining in the well in order to remove the top portion of the pipe string temporarily; running a milling device down to the flattened pipe string end and milling said end to reduce the diameter thereof; and removing the milling device and lowering a grappling device, over said milled pipe string end and lifting said pipe string from said supported position.
 2. The method set forth in claim 1, wherein said remaining drill string is removed by the steps of: lowering a spiral grapple downwardly over said milled end of said pipe string; positioning said spiral grapple about a pipe joint; and grappling said remaining pipe string at said pipe joint and raising same.
 3. The method set forth in claim 2, including the steps of: supporting said pipe string at a joint thereof; and positioning said grapple about said joint by landing the grapple on the rams of said annular blowout preventer.
 4. The method set forth in claim 1, including: milling the flared ears of said flattened drill string end to reduce the diameter of said flattened upper end to less than the diameter of a pipe string joint.
 5. The method set forth in claim 1, including: supporting said pipe string at by joint thereof; and limiting the final, milled diameter to the flattened pipe string end by landing the milling device on said blowout preventer rams. 